Re: [PATCH 2/2] drm/i915: Align the retire_requests worker to the nearest second

[Arjan van de Ven <arjan@linux.intel.com>]

On 10/5/2012 6:53 AM, Chris Wilson wrote:
> By using round_jiffies() we can align the wakeup of our worker to the
> nearest second in order to batch wakeups and reduce system load, which
> is useful for unimportant coarse tasks like our retire_requests.
> 
> Suggested-by: Arjan van de Ven <arjan@linux.intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c |   14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 8e05d53..706f481 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2084,6 +2084,11 @@ i915_gem_next_request_seqno(struct intel_ring_buffer *ring)
>  	return ring->outstanding_lazy_request;
>  }
>  
> +static unsigned long round_jiffies_delay(unsigned long delay)
> +{
> +	return round_jiffies_relative(delay) - jiffies;
> +}

this is buggy


> +
>  int
>  i915_add_request(struct intel_ring_buffer *ring,
>  		 struct drm_file *file,
> @@ -2155,7 +2160,8 @@ i915_add_request(struct intel_ring_buffer *ring,
>  		}
>  		if (was_empty) {
>  			queue_delayed_work(dev_priv->wq,
> -					   &dev_priv->mm.retire_work, HZ);
> +					   &dev_priv->mm.retire_work,
> +					   round_jiffies_delay(HZ));

when used like this


round_jiffies() rounds absolute jiffies towards the next second

round_jiffies_relative() already subtracts jiffies from the result, like
the helper that you're trying to invent here does ;=)

doing that double up is a bad idea.